This invention relates generally to optical interfaces for data communication and, more particularly, to optical interfaces which can be manufactured and aligned in a cost-effective manner, as well as to methods for aligning such optical interfaces.
Optical data communications technology has a number of advantages over wire technology. For example, bandwidth, data rate and response characteristics are superior to those of conventional wire technology. Optical technology is essentially immune to RFI (radio frequency interference) and EMI (electromagnetic interference) issues that plague wire technology. Shielding as in coaxial cables is not required, allowing the overall size and weight of systems to shrink.
Optical fiber telephone lines and world wide data links are replacing the bandwidth-limited wire technology. Likewise, optical technology, particularly optical interfaces for data communications, is highly desired in a variety of applications such as multi-component modules (MCMs), various printed circuit board (PCB) technologies, and integrated backplanes. Employing optical timing in radar transmit/receive modules to form phased array antennas is an objective in design of radar installations.
In such systems, electro-optical devices can be employed at the point of conversion from light to electronic transmission, and vice-versa. (As employed herein the term xe2x80x9clightxe2x80x9d is not limited to visible light, and includes optical wavelengths both above and below the range of visible light wavelengths). Electro-optical devices typically comprise semiconductor devices, which may be referred to as xe2x80x9cchipsxe2x80x9d or xe2x80x9cdiexe2x80x9d. Examples of optical emitters or transmitters include light emitting diodes (LEDs), laser diodes, and arrays of these used in automobile tail light applications. An example of an optical receiver is a photodiode. The integration of such electro-optical devices within high density interconnect structures, including the use of adaptive lithography techniques to produce optical interconnects, is disclosed in aforementioned Wojnarowski et al., U.S. Pat. Nos. 5,562,838 and 5,737,458.
Problems associated with micro-optical alignment prevent the economical usage of optical technology. Generally, micro-optical alignment is an expensive hand tuning operation. Thus, what is limiting a great number of potential applications is the ability to correctly align an optical die to an optical path, such as is represented by an optical fiber or by a corresponding optical die, as well as the ability to interconnect an optical assembly to a backplane.
In an exemplary embodiment of the invention, an array of optical emitters, such as laser diodes or light emitting diodes (LEDs), for example, and an optical receiver or an end of an optical fiber are positioned within a predetermined tolerance with reference to each other so as to establish an optical data communication path. One of the optical emitters provides the most optimum path. To search for and determine which emitter in the array of optical emitters provides the optimum optical path, that is, achieves the best alignment, the optical emitters are individually energized in a sequence, while monitoring an output signal of the optical receiver or of the optical fiber. Thus, the laser diode array, with redundant laser emitting cells, is energized in a scanning manner, while the receiver output signal is monitored for the best fit signal response. This may be done individually in a sequential manner, or may be done automatically as various subassemblies are assembled into a system, and additionally upon each repair or replacement operation. The scanning and monitoring may be performed by a setup align algorithm for post-assembly. For subsequent data communications, the optical emitter determined to achieve the best alignment is employed.
Conversely, in another exemplary embodiment of the invention, an array of optical receivers and an optical emitter are mechanically positioned within a predetermined tolerance with reference to each other to establish an optical data communication path. One of the optical receivers corresponds to the most optimum optical path from the optical emitter. To determine which receiver in the array of optical receivers corresponds to the most optimum optical path, in other words, which achieves the best alignment, the optical emitter is energized, and output signals of the optical receivers are measured. For subsequent data communications, the optical receiver determined to achieve the best alignment is employed.
The invention accordingly provides optical-to-electronic interfaces in a cost effective manner, and facilitates automating the alignment process between optical fibers, optical electronic assemblies, and optical connector interfaces to associated assemblies such as backplanes. The invention may be deployed in PC card and backplane assemblies, in combination with a variety of three-dimensional stacking technologies, and in a variety of other applications where critical alignment of optical subassemblies is important. The invention may also be employed to find related ends of long multi-fiber optical cables, such as under rivers and oceans. Labor intensive alignment operations are minimized in a manner suitable for production applications.